Crankshaft Counterweights

[Synchro909]

I am considering putting counterweights on a spare crankshaft I have. Big ends and mains are all 0.015 undersize so it's a good candidate. I have a set of weights I bought a few years ago from one of the parts suppliers. They are 5/8" thick and should be welded to the shaft but I've heard that a better result can be obtained by putting more weight on than what they provide and that this is done by bolting an extra weight to the sides of the ones I have so they can be removed for any future grinding of the journals. Does anybody have dimensions for these extra weights. I assume we put one each side of the welded on weights.
I think they would be 10mm (3/8" thick) and follow the curve of the larger diameter of the weights I have but how wide are they an how long? 3/8" will clear the con rod easily.
Anything else I should know???